July 21, 2010
Author: Trouts Staff
If there is one thing I have learned about fly fishing in the Rocky Mountain West, it is that nothing is constant. River levels rise and fall, insect hatches come and go, and a trout’s mood can be influenced by any number of outside variables, both tangible and not. While it would seem logical that late summer would be one of the more consistent times of year to fish, the reality is that there are evolving circumstances that can change the make up of a river and how fish will subsequently react. Knowing how to identify these variables, as well as understanding their subsequent influence on the productivity of a stream, is a paramount skill that every fly angler in Colorado should have. So let’s take a moment and discuss some of the key factors that influence the productivity of a river, particularly in late summer.
River Flow: While the flow of a river is in constant flux, it is from mid July to mid September where we see water flows play such a vital role in the productivity of a fishery. Too high and everything gets blown out leaving the fish scrambling trying to find suitable habitat. Too low and the fish begin to get stressed because they feel more vulnerable to predators. So it seems that we’re always looking for that elusive “prime” flow where the bugs are hatching, and the fish are happily feeding. So how do we know when that “prime” flow is? Unfortunately there isn’t a set standard or method to measure this; every river is different, and each will react differently to the rise and fall in flow. But if we understand where the water that fills our streams comes from, it becomes easier to calculate when these “prime” flows will be, particularly during the late summer months.
In the west, roughly 70% of our annual precipitation comes in the form of snow. So once the snow is gone, we are totally reliant on rainfall and cooler weather to help keep rivers at optimal levels. This year has been unique as we started out the summer with a state wide snowpack around 100% of average. We then quickly lost much of our snowpack in a short period of time right around the first weekend in June, when temperatures in the high country peaked in the upper 80’s and low 90’s. As a result, we experienced river levels that peaked at near 25 year highs on certain rivers. While these high flows are great for flushing out our streams, the mass exodus of our snowpack has ultimately left us very vulnerable to low flows and now 100% reliant on rainfall to help us get through the last months of summer. So what does this mean for late summer fishing here in Colorado? Pray for rain and cool weather!!!